In high-speed downlink packet access networks HSDPA, a so-called RMC AM protocol is responsible for reliable data transmissions in the layer 2 between the radio network controller RNC and a user terminal UE, WO 2009/058084 A2, Efficient Flow Control in a Radio Network Controller. Here, each RLC AM entity consists of a transmitting and a receiving side. An RLC AM entity can act either as a sender or a receiver depending on the implemented procedure, where the sender is the transmitter of RLC AM packet data units PDU and the receiver receives and processes transmitted PDUs.
Due to the reliable transmission of RLC AM, it may provide seamless handover and channel switching operations. Data packets which are lost between the radio network controller RNC and the user terminal UE due to bad radio or transport network TN link conditions are retransmitted, to avoid non congestion related packet loss, which is beneficial for transmission control protocol TCP in terms of utilizing network capabilities. On the other hand, RLC retransmissions can increase the round trip time RTT significantly such that timing constraints for transmission are difficult to be met. In addition, reliable packet delivery of RLC makes it hard to drop or re-order packets, e.g., to indicate transport network TN or radio congestion.
Further, when the buffers in the network are large, several hundreds of milliseconds, the receiving side of the RLC may request the retransmission of such RLC PDU that is not lost but waiting in the buffer to be served. In the case of HSDPA, such mechanism may result in many duplicate PDUs which are waiting in a priority queue PQ of the transmitter which further increases the load on the radio interface.
In consideration of the problems explained above, one solution which is proposed so far, see US 2002/0082023 A1, Method and Apparatus for Providing Adaptive Fast Radio Congestion Control, is to introduce an RLC retransmission prohibit timer in order to improve the efficiency of RLC in case of large buffer. The timer disables to retransmit a RLC PDU when a NACK of the PDU is received at the transmitter until the timer expires.
In view of the above, the problem underlying the present invention is to increase the utilization of the radio link and to provide a low complexity approach to retransmission control with respect to a fragmenting transmission protocol and a stream of data packets considered for data transmission.